How to draw an overlay on a SurfaceView used by Camera on Android?

问题:

I have a simple program that draws the preview of the Camera into a SurfaceView. What I'm trying to do is using the onPreviewFrame method, which is invoked each time a new frame is drawn into the SurfaceView, in order to execute the invalidate method which is supposed to invoke the onDraw method. In fact, the onDraw method is being invoked, but nothing there is being printed (I guess the camera preview is overwriting the text I'm trying to draw).

This is a simplify version of the SurfaceView subclass I have:

public class Superficie extends SurfaceView implements SurfaceHolder.Callback {  SurfaceHolder mHolder;  public Camera camera;  Superficie(Context context) {   super(context);   mHolder = getHolder();   mHolder.addCallback(this);   mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);  }  public void surfaceCreated(final SurfaceHolder holder) {   camera = Camera.open();   try {    camera.setPreviewDisplay(holder);    camera.setPreviewCallback(new PreviewCallback() {     public void onPreviewFrame(byte[] data, Camera arg1) {      invalidar();     }    });   } catch (IOException e) {}  }  public void invalidar(){   invalidate();  }  public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {   Camera.Parameters parameters = camera.getParameters();   parameters.setPreviewSize(w, h);   camera.setParameters(parameters);   camera.startPreview();  }  @Override  public void draw(Canvas canvas) {   super.draw(canvas);   // nothing gets drawn :(   Paint p = new Paint(Color.RED);   canvas.drawText("PREVIEW", canvas.getWidth() / 2,     canvas.getHeight() / 2, p);  } }

回答1:

SurfaceView probably does not work like a regular View in this regard.

Instead, do the following:

1. Put your SurfaceView inside of a FrameLayout or RelativeLayout in your layout XML file, since both of those allow stacking of widgets on the Z-axis
2. Move your drawing logic into a separate custom View class
3. Add an instance of the custom View class to the layout XML file as a child of the FrameLayout or RelativeLayout, but have it appear after the SurfaceView

This will cause your custom View class to appear to float above the SurfaceView.

See here for a sample project that layers popup panels above a SurfaceView used for video playback.

回答2:

Try calling setWillNotDraw(false) from surfaceCreated:

public void surfaceCreated(SurfaceHolder holder) {     try {         setWillNotDraw(false);          mycam.setPreviewDisplay(holder);         mycam.startPreview();     } catch (Exception e) {         e.printStackTrace();         Log.d(TAG,"Surface not created");     } }  @Override protected void onDraw(Canvas canvas) {      canvas.drawRect(area, rectanglePaint);     Log.w(this.getClass().getName(), "On Draw Called"); }

and calling invalidate from onTouchEvent:

public boolean onTouch(View v, MotionEvent event) {      invalidate();     return true; }

回答3:

I think you should call the super.draw() method first before you do anything in surfaceView's draw method.

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